i always thought then when you build a hybrid, the final displacement was 2.5L. but as i was reading around, i saw places where it said that it was only 2.1 or 2.2 liters. Could someone clear this up for me

That is not true. Those are stroker kits for the 2.0L that give you that final displacement. A hybrid uses the physical block and pistons out of the larger 2.5L engine so it gives the same displacement, you just keep your heads. Heads don't really effect displacement much. I am drastically over-simplifying but hopefully that helps.